In recent years, the mainstream of a data communication method which a mobile communications system uses has been changing from a circuit switching method to a packet communication method.
While, in general, the packet communication method is based on a continuous connection, there is a limit to the available capacity of a battery which a mobile terminal in a mobile communications system can carry.
Therefore, in a case in which the mobile communications system employs a packet communication method (a continuous connection), it is necessary to achieve low power consumption in a mobile terminal.
As a standardization organization of mobile communications systems, the 3GPP (3rd Generation Partnership Project) exists.
Currently, in the 3GPP, a UTRAN system (Release7) and an Evolved RAN system (E-UTRAN, LTE: Long Term Evolution) which are mobile communications systems of the next version have been under debate, and reduction in the power consumption in the packet communication method has also been under debate on the spot.
It has been determined in the debate that because, in a mobile terminal using the packet communication method, a case in which there exist no transmission data and no received data can occur even if a wireless section is being connected, a newly provision of a state of supporting low power consumption in a mobile terminal and an operation of supporting low power consumption in a mobile terminal has been determined.
For an LTE system, a state 1 “Idle” in which a mobile terminal is during inactivity at an RRC level, and a state 2 “Active (in a broad sense)” in which a mobile terminal is during active are defined. Nonpatent reference 1 shown hereafter discloses introduction of a new state 2-A “Active (in a narrow sense)” and a state 2-B “DRX/DTX operation period during Active” into during “Active (in a broad sense)”, as shown in FIG. 13.
Furthermore, nonpatent reference 2 shown hereafter describes that it is possible to dispose a DRX/DTX period (DRX/DTX period) in RRC_Connected (corresponding to the state 2 of FIG. 13) in order to achieve low power consumption in a mobile terminal.
The state 1 of FIG. 13 is called “Idle”, “LTE_Idle”, “RRC_Idle”, “NAS_Idle”, or the like, and a mobile terminal placed in the state 1 of FIG. 13 performs a receiving operation in a DRX cycle which is set up by NAS (Non-Access Stratum) (i.e., in a cycle different from the DRX cycle of a DRX/DTX operation period during Active (the state 2-B of FIG. 13)). More specifically, the mobile terminal performs a Paging operation.
The state 2 of FIG. 13 is called “Active”, “LTE_Active”, “RRC_Active”, “RRC_Connected”, “Connected”, “NAS Active”, or the like.
The state 2-A of FIG. 13 is called “Active”, “MAC_Active”, or the like.
The state 2-B of FIG. 13 is called “Dormant”, “MAC_Dormant”, “DRX/DTX period (DRX/DTX period)”, “DRX/DTX period during Active”, “DRX/DTX period during Connected”, or the like, and, in this state, an operation for achieving low power consumption in a mobile terminal during Active is carried out (for example, a stop of transmission or reception of data (user data and control data) is performed temporarily).
Nonpatent reference 3 shown hereafter discloses a technology of, during a DRX/DTX operation period during Active (the state 2-B of FIG. 13), carrying out a process of signaling both a period during which a DRX operation is performed and a period during which a DTX operation is performed by using MAC (Medium Access Control) by a base station.
Patent references 1 shown hereafter discloses a technology of switching a cycle in which a mobile terminal transmits a CQI (Channel Quality Indicator) to a base station between a high-speed one and a low-speed one according to whether or not transmission of downlink data has been performed, though the cycle differs from the DTX cycle in a DRX/DTX operation period during Active (the state 2-B of FIG. 13). Thereby, effective use of the uplink radio resources is achieved.
Nonpatent reference 4 shown hereafter discloses a technology of making a mobile terminal check to see whether there exist data destined for the mobile terminal itself in a DRX cycle during Active (the state 2 of FIG. 13) by using a downlink scheduling channel.
Nonpatent reference 6 shown hereafter describes a notification method of notifying a DRX period.
The notification method of notifying a DRX period will be explained with reference to FIG. 14.
Information indicating a DRX period is included in control data (e.g., an L1/L2 control signal) which associates first-time transmission data (user data) from a base station.
When the mobile terminal fails in reception of the first-time transmission data transmitted from the base station, the mobile terminal transmits a HARQ-compliant Nack signal (negative response signal) to the base station.
When receiving the Nack signal transmitted from the mobile terminal, the base station retransmits the same data as the first-time transmission data to the mobile terminal. The information indicating a DRX period is not included in the control data which associates this retransmission.
When succeeding in the reception of the retransmission data transmitted from the base station, the mobile terminal starts a timer A while transmitting a HARQ-compliant Ack signal (ACK signal) to the base station.
When receiving the Ack signal transmitted from the mobile terminal, the base station starts a timer A.
After the timers A are expired, the mobile terminal and the base station start their DRX operations.
Nonpatent reference 8 shown hereafter discloses a DRX operation in a case in which two DRX cycles are set up.
Nonpatent reference 5 shown hereafter discloses a technology of judging whether to carry out an operation with low power consumption according to mobile terminal capability information (UE Capabilities) showing the capabilities of a mobile terminal, though the purpose of the technology differs from those disclosed in the above-mentioned nonpatent references 1 to 4 and the patent reference 1.
Control signals which are used to enable communications between a mobile terminal and a base station via a radio link include an upper layer signal, such as an “L3 control signal” (a Layer3 control signaling or an L3 message), and a signal which is called an “L1/L2 control signal” (a Layer1/Layer2 control signaling).
An L3 control signal is typically notified from an upper layer, such as an RRC layer, at a time of initial transmission including a time of occurrence of a call connection (RRC Connect), and is used to perform a setup of uplink or downlink channels via the downlink or allocation of radio resources via the downlink.
In contrast, an L1/L2 control signal is frequently exchanged between a mobile terminal and a base station via both the uplink and the downlink, and includes an uplink scheduling request signal which a mobile terminal outputs to make a request of a base station for allocation of the radio resources via the uplink. Also at a time when the radio resources are irregularly changed in response to a request to change the data size or a request for the quality of the communication path, the time including a time of occurrence of a call connection and a time of continuation, an L1/L2 control signal is used.
An L1/L2 control signal includes an Ack signal/Nack signal which either a base station or a mobile terminal sends back to the party on the other end of the connection when receiving data via uplink or downlink to answer whether either the base station or the mobile terminal has received the data correctly, and a quality information CQI (Channel Quality Indicator) showing the quality of the received data or the quality of the communication path.
Nonpatent reference 7 shown hereafter shows that, in an uplink reference signal (Reference Signal), two types of signals including a reference signal used for demodulation (Demoduration) and synchronous detection (Detection), and a reference signal (Sounding Reference Signal) used for measurement of the quality of an uplink channel exist. The Sounding Reference Signal (Sounding RS) is transmitted from a mobile terminal (UE) to a base station (eNB) in order for the base station to measure the communication quality of the uplink.
The following nonpatent reference 9 discloses that only time division multiplexing (Time Division Multiplexing: TDM) is used as a method of transmitting data for a E-MBMS (Evolved Multimedia Broadcast Multicast Service) and services other than the E-MBMS (non-MBMS and non-EMBMS). Units in which the time division is carried out is set to be subframes (Subframes).
The E-MBMS is a multicast and broadcast type multimedia service.
In this service, a large-volume broadcast content, such as a news content, a weather forecast content, or a mobile broadcast content, is transmitted to a plurality of mobile terminals.
A base station maps E-MBMS data onto either a DL-SCH (Downlink Shared Channel) or an MCH (Multicast Channel), and then transmits the E-MBMS data to mobile terminals.
Furthermore, LTE not only provides a broadcast type communication service (except the E-MBMS (non-MBMS)), but also provides a communication service to an individual mobile terminal among a plurality of mobile terminals. A communication service provided to an individual mobile terminal is called a Unicast service.
Nonpatent reference 10 shown hereafter discloses that either only one leading symbol or only two leading symbols included in a subframe which is allocated to the E-MBMS through time division multiplexing is used by a Unicast service.
However, the nonpatent references 1 to 3 and the patent reference 1 do not disclose any concrete method of effectively achieving low power consumption in a mobile terminal in a DRX/DTX operation period during Active (a state 2-B as shown in FIG. 13).
More specifically, the nonpatent references 1 and 2 disclose newly establishment of a state (the state 2-B shown in FIG. 13) for supporting low power consumption in a mobile terminal, but does not disclose any method of efficiently achieving low power consumption in a mobile terminal in a DRX/DTX operation period during Active (the state 2-B shown in FIG. 13) which is newly established.
Furthermore, the nonpatent reference 3 discloses the technology of signaling information indicating a period during which a DRX operation is performed and a period during which a DTX operation is performed in a DRX/DTX operation period during Active (the state 2-B shown in FIG. 13) by using the MAC of a base station, as mentioned above, but does not disclose any method of setting up DRX/DTX cycles in order to efficiently achieve low power consumption in a mobile terminal.
In addition, the notification method of notifying a DRX period disclosed by the nonpatent reference 6 differs from a notification method of notifying a DRX period which will be disclosed by the present invention.
Furthermore, a problem with the method disclosed by the nonpatent reference 6 is that a base station has to carry out scheduling in order to determine a timing (i.e., a DRX period end timing) at which the base station starts a DRX operation every time when the base station receives a Nack signal from a mobile terminal (“a time (i)”, “a time (ii)”, and “a time (iii)” shown in FIG. 14), and therefore the load of the scheduling becomes heavy. Thus, the nonpatent reference 6 is not aimed at notifying the information indicating a DRX period while reducing the scheduling load of the base station, and does not offer any suggestion about this purpose.
In a DRX operation in the case in which two DRX cycles are set up, which is disclosed by the nonpatent reference 8, any application of HARQ is not taken into consideration at all.
Therefore, a problem with the method of notifying the DRX cycle information by using an L1/L2 control signal together with the first-time transmission data, notifying the DRX cycle information at a time of a setup of a radio bearer, or determining the DRX cycle information in advance, in a conventional way is that when retransmission based on HARQ exceeds this DRX cycle, it becomes impossible to make a transition to a DRX operation.
The nonpatent reference 9 and 10 describe nothing about a DRX operation (a DRX operation during Active).
Furthermore, these references also disclose nothing about what kind of information is notified using a symbol available for a Unicast service in a subframe allocated to the E-MBMS.
The patent reference 1 discloses the technology of switching a cycle in which a mobile terminal transmits a CQI to a base station between a high-speed one and a low-speed one according to whether or not transmission of downlink data has been performed, but discloses nothing about a signaling between the mobile terminal and the base station for the switching of the cycle between a high-speed one and a low-speed one. The technology disclosed by the patent reference 1 is the one in which no operation with low power consumption is introduced into the operation of a mobile terminal during Active (the state 2 as shown in FIG. 13).
Next, the nonpatent reference 4 discloses the technology of making a mobile terminal check to see whether there exist data destined for the mobile terminal itself in a DRX cycle during Active (the state 2 as shown in FIG. 13) by using a downlink scheduling channel, as mentioned above. In other words, in a mobile terminal during a DRX/DTX operation period during Active (the state 2-B as shown in FIG. 13), a period during which the mobile terminal is unable to receive any downlink data from a base station exists.
Therefore, even when a base station desires to transmit downlink data to a mobile terminal during a DRX/DTX operation period during Active (the state 2-B as shown in FIG. 13), the base station cannot transmit any data to the mobile terminal until a preset cycle has elapsed.
Therefore, the throughput of the mobile terminal decreases, and, even if it is preferable to give a higher priority to the throughput of the mobile terminal than to achievement of low power consumption in the mobile terminal, any improvement in the throughput cannot be achieved.
Nonpatent reference 5 shown hereafter discloses a technology of judging whether a mobile terminal should carry out an operation with low power consumption according to the mobile terminal capability information (UE Capabilities) in order to enable application to a case in which a higher priority should be given to the throughput of the mobile terminal.
However, in the current technology, the mobile terminal capability information (UE Capabilities) is a value specific to each mobile terminal.
The mobile terminal capability information (UE Capabilities) is notified from the mobile terminal to the network at a time of an RRC (Radio Resource Control) connection (e.g., at a time of attach, at a time of calling, and at a time of location registration).
Therefore, in accordance with the current technology, because a parameter showing which achievement of low power consumption in a mobile terminal or an improvement in the throughput of the mobile terminal should be given a higher priority is specific to each mobile terminal, and the timing at which a notification of the parameter can be made is restricted, it is difficult to effectively achieve low power consumption in the mobile terminal during a DRX/DTX operation period during Active (a state 2-B as shown in FIG. 13).    [Nonpatent reference 1] 3GPP technical specifications TR25.913 V7.2.0    [Nonpatent reference 2] 3GPP technical specifications TR25.813 V0.9.0    [Nonpatent reference 3] 3GPP contributions R2-060888    [Nonpatent reference 4] 3GPP contributions R2-060591    [Nonpatent reference 5] 3GPP contributions R2-060846    [Nonpatent reference 6] 3GPP contributions R2-070279    [Nonpatent reference 7] 3GPP technical specifications TR25.814 V7.0.0    [Nonpatent reference 8] 3GPP contributions R2-070265    [Nonpatent reference 9] 3GPP contributions R1-071245    [Nonpatent reference 10] 3GPP contributions R2-070701    [Patent reference 1] JP, 2003-204298, A
Because conventional mobile communications systems are constructed as mentioned above, they make it possible to introduce the state 2-B, i.e., a “DRX/DTX operation period during Active” into the state 2, in which the system is operating at an RRC level, i.e., an “Active (in a broad sense).” A problem is, however, that neither a method of efficiently achieving low power consumption in a mobile terminal nor a method of setting up DRX/DTX cycles is defined, and therefore low power consumption cannot be necessarily achieved efficiently in a mobile terminal.
The present invention is made in order to solve the above-mentioned problems, and it is therefore an object of the present invention to provide a mobile communications system which can achieve low power consumption in a mobile terminal efficiently, and a mobile terminal which can achieve low power consumption.